Many modulation schemes generate I and Q components from complex signals. The I and Q signals are phase shifted relative to each other. For example, the I and Q signals may be orthogonal. The I and Q components may be amplified by power amplifiers. In order to improve efficiency of the power amplifiers, the combined I and Q amplitude is reduced at the baseband using crest factor reduction (CFR) techniques. In summary, crest factor reduction reduces or suppresses peaks in amplitudes of the complex signals.
Some modulation schemes, such as time-interleaved pulse width modulation and spatially combined IQ modulation, use amplifiers that are peak constrained by amplitudes of the individual I and Q components and not amplitudes of the combined I and Q signals. Traditional crest factor reduction, which reduces the combined I and Q amplitude, does not yield optimal power amplification output power and efficiency when used with these modulation schemes.